Commonly assigned U.S. patent application Ser. No. 09/532,432 now U.S. Pat. No. 6,519,500 and Ser. No. 10/088,040 now U.S. Pat. No. 6,814,823, the entire content of each being incorporated herein by reference, disclose systems and methods for fabricating objects by consolidating material increments in accordance with a description of the object using a process that produces an atomically clean faying surface between the increments without melting the material in bulk. Ultrasonic, electrical resistance, and frictional methodologies, and combinations thereof, may be used for such consolidation.
According to these previous disclosures, the material increments are placed in position to shape the object by a material feeding unit. The raw material may be provided in various forms, including flat sheets, segments of tape, strands of filament or single dots cut from a wire roll. The material may be metallic or plastic, and its composition may vary discontinuously or gradually from one layer to the next, creating a region of functionally gradient material. Plastic or metal matrix composite material feedstocks incorporating reinforcement materials of various compositions and geometries may also be used.
If excess material is applied due to the feedstock geometry employed, such material may be removed after each layer is bonded, or at the end of the process; that is, after sufficient material has been consolidated to realize the final object. A variety of tools may be used for material removal, depending on composition and the target application, including knives, drilling or milling machines, laser cutting beams, grinding, EDM, chemical etch, or ultrasonic cutting tools.
The material increments are fed sequentially and additively according to a computer-model description of the object, which is generated by a computer-aided design (CAD) system, preferably on a layer-by-layer basis. The CAD system, which holds the description of the object, interfaces with a numerical controller, which in turn controls one or more actuators. The actuators impart motion in multiple directions. Three orthogonal directions may be used or five axes, including pitch and yaw as well as XYZ, may be appropriate for certain applications, so that each increment (i.e., layer) of material is accurately placed in position and clamped under pressure.
During these additive manufacturing or free-form fabrication processes, it is often important to provide a support material to the part being produced. This is most often the case when enclosed volumes, or cantilevered sections are being produced, although other types of features with less aggressive unsupported geometries also require the use of supports. There are two types of support structures in free form fabrication, which can be classified as intrinsic and extrinsic.
Intrinsic support structures are those which are essentially produced as a result of the process itself. A classic example of this situation is that pertaining in selective laser sintering or 3D printing, wherein a powder layer is spread across an entire build volume. An operation is performed on certain regions of the powder (i.e., passing a laser over it to melt the powders, or printing binder over it to cause the particles to adhere to each other), which correspond to the cross section of the layer of the part being built to cause the particles to adhere. The remainder of the unaffected powder remains in place as another layer is spread and the process repeated. This mass of unbound powder serves the function of supporting additional layers of material as they are deposited.
Extrinsic support are those in which a second material is used to support the growing structure (examples include shape deposition modeling and inkjet based systems), or in which special support structures are built using the build material or a second material (examples include fused deposition modeling and stereolithography) which are later cut off. In general, intrinsic supports have advantages over the extrinsic types, as they are simpler to implement, since they do not require the supply of a second material.